1. Field of the Invention
The present invention relates to a solid electrolytic capacitor using a valve metal or an alloy thereof as an anode.
2. Description of the Related Art
There has been known a solid electrolytic capacitor including: an anode formed of a valve metal or an alloy thereof; and a metal oxide layer formed as a dielectric layer on the surface of the anode by anodizing the anode in a phosphoric acid solution or the like. An electrolyte layer formed of manganese dioxide or the like is formed on the dielectric layer thus formed by the anodization. However, there has been a problem that an equivalent series resistance (ESR) becomes large because the conductivity of manganese dioxide is smaller than that of a metal or the like. Accordingly, it has been proposed that an ESR is reduced by using a conducting polymer as an electrolyte layer in place of manganese dioxide.
However, in the solid electrolytic capacitor using a conducting polymer as an electrolyte layer, there has been a problem of decreasing capacitance when the solid electrolytic capacitor is preserved under high temperature.
Japanese Patent Application Publication No. Hei 5-136009 proposes that a buffer layer formed of a low stress resin is provided inside a resin outer package in order to alleviate mechanical stress caused by contraction of the resin outer package when the resin outer package, which is formed for sealing the entire device, is molded. However, since such a buffer layer is used for alleviating the mechanical stress when the resin outer package is molded, the decrease in capacitance of the solid electrolytic capacitor preserved under high temperature cannot be suppressed by the buffer layer.
In addition, Japanese Patent Application Publication No. Hei 8-148392 proposes that a buffer material is provided on a surface of a device, facing the gate of the mold, in order to protect the device from mechanical shock due to injection pressure when a resin is molded. However, this buffer material is also for alleviating the mechanical shock when a resin compact is molded, and thus cannot suppress the decrease in the capacitance of the solid electrolytic capacitor preserved under high temperature.